1. Field of the Invention
The present invention relates to an image forming apparatus, a surface property reforming sheet, and a method for forming an image.
2. Description of the Related Art
In related art at present, leading examples of thermal line printers include sublimation type, fusion type, and heat sensitive type printers.
In thermal heads used in the above-described printers, a plurality of heater elements (resistance elements) are arranged in a line. The plurality of heater elements are energized selectively in accordance with levels of gray scale, and image printing is conducted on various types of recording sheet through the use of the thermal energy generated at that time.
Regarding the sublimation type, image printing is conducted by holding an ink ribbon and a recording sheet fed to a platen with a thermal head, energizing and driving heater elements in the thermal head selectively, and sublimating an ink on the ink ribbon so as to transfer the ink to the recording sheet. In general, the above-described ink ribbon is wound around a supply reel and a take-up reel and has a configuration in which ink layers of a plurality of different colors and a protective material layer (L) are sequentially repeatedly formed on a base film along the feeding direction of the ink ribbon. The above-described ink layers includes, for example, ink layers of each of yellow (Y), magenta (M), and cyan (C).
The above-described protective material layer protects an image produced by the above-described ink layers transferred to the recording sheet, and it is possible to form a transparent film layer on the above-described image through thermal transfer so as to improve the chemical agent and solvent resistance, the oil and grease resistance, the friction resistance, and the like. Furthermore, it is also possible to enhance the surface glossiness of the image and improve the quality.
Moreover, frosted or matte expression is also possible by controlling energy applied to the thermal head at a stage of transfer of the protective material layer or conducting transfer on the basis of a specific pattern. In this manner, the surface property can be selected to meet the preferences of the user.
However, the above-described protective material layer is peeled off a release layer which has been formed on a base film of a thermal transfer sheet and which exhibits insufficient smoothness and is transferred in such a way that the peeling surface thereof becomes a surface of an image print. Consequently, the level of glossiness is lower than that of a silver halide photograph.
Regarding this issue, surface property reforming technologies have been disclosed, in which desired surface properties including the above-described improved surface glossiness can be provided to image prints.
In one of the surface property reforming technologies (first related art), distribution of glossiness is provided to a surface of a sheet member in accordance with the image information (the brightness, the density of image, the color tone of image, the size of image, and combinations thereof) and, thereby, a three-dimensional appearance is given to an image print.
It is described that an uneven shape of a sheet member can be controlled by combining an image heating device and surface properties of a plurality of contact members and, as a result, desired distribution of the glossiness can be provided on a sheet member surface. It is described that when the surface of the contact member (endless belt) is a mirror-finished surface, the glossiness of the heated portion is improved and the glossiness of the other portion remains at a normal level and, therefore, a three-dimensional appearance can be given to the image (refer to, for example, Japanese Unexamined Patent Application Publication No. 2005-219388).
Furthermore, in one of the above-described technologies (second related art), a configuration is disclosed, in which a sheet member heating device for transferring surface properties of a contact member to a sheet member heated in a sheet member preheating portion and a sheet member cooling device for cooling the above-described sheet member while the sheet member is in contact with the above-described contact member are included.
In this technology, an endless belt is adopted as the above-described contact member, and the surface thereof is finished to have desired surface properties (one of a glossy surface, a matte surface, and an embossed surface). It is described that a record image on hand can easily be converted to an image having desired surface glossiness (high gloss, medium gloss, matte, and the like) in this manner (refer to, for example, Japanese Unexamined Patent Application Publication No. 2004-279568).
Moreover, one of the above-described technologies (third related art) has a configuration in which a pressure and heat treatment is conducted while a recording sheet, a surface property reforming sheet, and an ink ribbon are sandwiched in such a way as to be stacked sequentially at a position of image printing. This technology is devised in such a way that an opening portion is provided in a part of the above-described surface property reforming sheet and is used when pressure and heat are applied to the ink ribbon.
That is, in the case where image printing and a lamination (formation of a protective layer) treatment are conducted, the above-described opening portion is aligned in such a way as to face a thermal head and, thereby, a thermal transfer sheet is allowed to come into direct contact with the recording sheet. In the case where a surface state of the transferred protective material layer is reformed, it is favorable that a desired portion of the above-described surface property reforming sheet is used and the pressure and heat treatment is conducted by using the same thermal head while the ink ribbon is interposed. At that time, if the thermal transfer sheet is aligned with a used part of the protective material layer, the time taken for feeding (taking up) the thermal transfer sheet becomes minimum, so that setting can be completed speedily. Furthermore, since the above-described protective material layer is wholly transferred to the recording sheet, the used part thereof is in a state of being consumed uniformly and, therefore, it is favorable.
This technology has a simple configuration as compared with other technologies because the pressure and heat treatment with respect to the ink ribbon and the pressure and heat treatment with respect to the surface property reforming sheet can be conducted with the same thermal head. Along with that, miniaturization, cost reduction, and the like of the apparatus can also be expected.
In the above-described third related art, apprehension remains about the timing of the surface property reforming treatment. In this timing, as described above, the used part of the protective material layer (or ink layer) and the surface property reforming sheet are subjected to the pressure and heat treatment while they are stacked on top of each other.
Regarding the above-described used part, most of the protective material layer is peeled off the base film through transfer. Consequently, a release layer thereunder is in the state of being exposed in a wide range. The range of formation of the protective material layer is originally a region slightly larger than the sheet size applied. Therefore, strictly, as shown in FIG. 6, an unreleased portion 39 indicated as a diagonally shaded portion remains in the marginal portion of the protective material layer 35 of the thermal transfer sheet 30 in any way, while the marginal portion is a used part, but is not included in the transfer range.
In addition, in the case where the above-described surface property reforming treatment is conducted in the state in which the unreleased portion 39 of the above-described protective material layer 35 remains, the unreleased portion 39 of the above-described protective material layer 35 may be transferred to the surface property reforming sheet so as to cause inconveniences.
More specifically, the surface property reforming sheet and the thermal transfer sheet may be adhered through the pressure and heat treatment in the unreleased portion of the protective material layer so as to cause defective peeling after the surface property reforming treatment.
Furthermore, the unreleased portion of the protective material layer, which is adhered to the surface property reforming sheet side through transfer, may be accumulated by repetition of the treatment, so that an application of a uniform pressure and heat treatment to the recording sheet becomes difficult.
Because of these inconveniences, for example, desired glossiness may not be obtained, and there may be variations in a matte state. Therefore, the surface property reforming treatment may become defective and there is apprehension about the long term stability.
On the other hand, if the surface property reforming sheet is formed from a polyimide film (for example, UPILEX: produced by UBE INDUSTRIES, LTD.) exhibiting low adhesion to other substances, even when the protective material layer becomes into a state of being softened to some extent and coming into intimate contact in the surface property reforming treatment, it is possible to allow an occurrence of the transfer to become difficult.
However, the situation is different from the unreleased portion, which remains on the ink ribbon, of the laminating layer also serving as a protective material.
In general, in order to obtain stable property of lamination on the recording sheet after the image is formed, the laminating layer configured to have at least two layers is used. That is, regarding an uppermost layer (L3 layer) relative to the base film, a material exhibiting excellent adhesion to the recording sheet is used in forming (laminating) a protective layer, and a material which is easily peeled off a release layer is used for a lowermost layer (L2 layer) in contact with the release layer. Consequently, it is made possible to form a stable protective material layer on an image formation surface of the recording sheet and obtain a state excellent in releasability from the thermal transfer sheet.
The protective material layer with which the polyimide film comes into contact in the surface property reforming treatment of an image print is the L2 layer, and this layer and the polyimide are difficult to adhere to each other. However, a layer, which comes into contact with the polyimide film, of the unreleased portion of the protective material layer remaining on the thermal transfer sheet side is the L3 layer exhibiting excellent adhesion. Therefore, use of polyimide exhibiting low adhesion is not satisfactory because transfer to the surface property reforming sheet may occur under the influence of variations in the ambient environment, repetition of the treatment, and the like.